Silicon and silicon/germanium light-emitting device, methods and systems

ABSTRACT

A light-emitting device and optical communication system based on the light-emitting device is disclosed. The light-emitting device is formed in a float-zone substrate. The light-emitting device includes on the substrate lower surface a reflective layer and on the upper surface spaced apart doped regions. The portion of the upper surface between the doped regions is textured and optionally covered with an antireflection coating to enhance light emission. The light-emitting device can operate as a laser or as a light-emitting diode, depending on the reflectivities of the antireflection coating and the reflective layer.

RELATED APPLICATION(S)

This application is a Divisional of U.S. application Ser. No. 10/140,255filed on May 6, 2002 which is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to light-emitting devices formed in Si orSi/Ge and to optical communications systems employing same.

BACKGROUND INFORMATION

Modern computers are formed from a variety of different types ofintegrated circuit (IC) chips, such as controllers, central processingunits (CPUs) and memory. On-chip and chip-to-chip interconnectionswithin a computer are typically made with metal wires. As ICs becomemore integrated, the wires becomes narrower and more closely spaced.This results in a higher resistance in the wires and a highercapacitance between wires, which act to slow the electrical signal andrequires more electrical power. The degree to which the electricalsignal is slowed is also proportional to the square of the length of thewire. Such signal delays negatively impact the performance of IC chipsand the computer as a whole.

To solve this problem, in-chip and chip-to-chip optical interconnectionsusing light sources and waveguides have been proposed. In an opticalinterconnection system, an electrical signal from the chip is convertedto an optical signal emitted by a light source. The light then travelsover a waveguide to a detector, which converts the received light backto an electrical signal. The speed of an optical interconnection is muchfaster than the flow of electrons in a wire and scales linearly with thelength of the optical interconnection.

Such optical interconnection systems generally require an external lightsource, i.e., one not integrally formed with the IC chip. This isbecause Si and Si/Ge, the materials presently used to form IC chips,have not been considered suitable for forming integral light sourcesbecause they have an indirect bandgap. Instead, external sources withdirect bandgap semiconductors, such as vertical cavity surface emittinglasers (VCSELS) formed from AlGaAs/GaAs or strained InGaAs/GaAsquantum-well devices have been used. While these light sources areeffective, they need to be separately packaged and interfaced with andaligned to the waveguide, as well as to other devices on the IC chip.This makes for a relatively complicated and expensive on-chip orchip-to-chip optical communication system.

Further complicating chip-to-chip communications is the limited numberof contact pads that can be fabricated onto a chip, as well as thelimited available chip area. As IC chips increase in sophistication,more and more input/output leads (e.g., pins or balls) are required toaccommodate the larger number of bits and inputs/outputs for otherapplications.

What is needed is a cost-effective optical interconnection system foron-chip and chip-to-chip communication that utilizes a light source anddetector formed integral with conventional Si or Si/Ge semiconductorsubstrates and that is compatible with standard IC fabricationprocesses.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a float-zone Si or Si/Ge substrate;

FIG. 2 is the float-zone substrate of FIG. 1, processed to form an oxideand reflective layer on a portion of the substrate lower surface;

FIG. 3 is the substrate of FIG. 2, further processed to form n+ and p+doped regions in the substrate upper surface;

FIG. 4 is the substrate of FIG. 3, further processed to form insulatorson the substrate upper surface over a portion of the n+ and p+ dopedregions;

FIG. 5 is the substrate of FIG. 4, further processed to form metalcontacts over the insulators and over the exposed portion of the n+ andp+ doped regions;

FIG. 6 is the substrate of FIG. 5, further processed to form a texturedportion in the upper surface between the n+ and p+ doped regions;

FIG. 7 is the substrate of FIG. 6, further processed to form anantireflection coating over the textured portion of the upper surface,thereby completing the formation of the light-emitting device of thepresent invention;

FIG. 8A is a plan view of an example embodiment of an on-chip opticalcommunication system that uses the light-emitting device of FIG. 7;

FIG. 8B is cross-sectional view of the system of FIG. 8A;

FIG. 9A is an example embodiment of forming a channel optical waveguidefor the system of FIG. 8A;

FIG. 9B is an example embodiment of forming the optical waveguide forthe system of FIG. 8A;

FIG. 9C is an example embodiment of forming the optical waveguide forthe system of FIG. 8A using a photosensitive polymer;

FIG. 10 is a close-up plan view of the light-emitting portion of anotherembodiment of an on-chip optical communication system as an alternateembodiment of the system of FIG. 8A, where the light-emitting device isan LED and where the system includes an optical modulator to modulatethe light from the LED;

FIG. 11 is a plan view of multiple optical communication systems formedon an IC chip;

FIG. 12A is a plan view of a chip-to-chip communication system that usesthe light-emitting device of FIG. 7; and

FIG. 12B is a side view of the system of FIG. 12A.

DETAILED DESCRIPTION

In the following detailed description of the embodiments of theinvention, reference is made to the accompanying drawings that form apart hereof, and in which is shown by way of illustration specificembodiments in which the invention may be practiced. These embodimentsare described in sufficient detail to enable those skilled in the art topractice the invention, and it is to be understood that otherembodiments may be utilized and that changes may be made withoutdeparting from the scope of the present invention. The followingdetailed description is, therefore, not to be taken in a limiting sense,and the scope of the present invention is defined only by the appendedclaims.

With reference to FIGS. 1-7 described briefly above, a method of formingan example embodiment of the light-emitting device of the presentinvention is now described.

In FIG. 1, a substrate 20 with an upper surface 22 and a lower surface24 is provided. In one embodiment, the substrate is float-zone. Inparticular, in one-example embodiment, the substrate is float-zonesilicon (Si), while in another example embodiment the substrate isfloat-zone silicon/germanium (Si/Ge). Use of a float-zone substrate ispreferred because such a substrate has few if any oxygen impurities,which can cause bulk defects that contribute to non-radiative carrierrecombination. Substrate 20 can be p-type or n-type.

In FIG. 2, a dielectric layer 40 is formed on lower surface 24. In anexample embodiment, the dielectric layer includes an oxide formed byheating lower surface 24 in an oxygen atmosphere at high temperature.Example oxides include SiO₂ and Al₂O₃. In another example embodiment,dielectric layer includes a nitride.

A reflective layer 50 is then formed over the dielectric layer. In anexample embodiment, reflective layer 50 is a metal, such as aluminum.Further in an example embodiment, the reflective layer is formed bymetalization. The dielectric layer serves to electrically insulate thereflective layer from the substrate.

In FIG. 3, spaced apart doped regions 60 and 62 are formed in uppersurface 22 of substrate 20. In an example embodiment, the doped regionsare n+ and p+. Example n-type dopants are As, P and N, while examplep-type dopants are B, BF₂ ⁺, Ga and Al.

The doped regions define a surface region 66 in between the dopedregions. In one embodiment, gas source diffusion is used to form thedoped regions. In another embodiment, ion-implantation is used, followedby an anneal step to eliminate any crystal dislocations that couldcontribute to non-radiative carrier recombination. In FIG. 4, insulators70 and 72 are formed atop upper surface 22 over respective portions ofthe doped regions 60 and 62, leaving exposed portions 74 and 76 of thedoped regions. In an example embodiment, insulators 70 and 72 are formedby selectively depositing SiO₂.

In FIG. 5, metal contacts 80 and 82 are formed over insulators 70 and 72to contact exposed portions 74 and 76, respectively. The metal contactsmay be formed from any one of a number of conductors, such as W, Al or asilicide. The metal contacts are also designed to provide a relativesmall amount of surface area contact. In an example embodiment, thecontact surface area is about 1% or less of the total upper surface areaof the light-emitting device.

In FIG. 6, at least a portion of surface region 66 is textured (i.e.,roughened) to form a textured surface 90. The texturing is performed toincrease the surface area to facilitate the emission of light 94 fromthe device. In an example embodiment, the textured surface is formed byetching with KOH.

In FIG. 7, in an example embodiment an antireflection (AR) coating 100is optionally formed over textured surface 90 to further enhance lightemission from the device. The AR coating material and thickness isselected for the wavelength of light generated, and may include multiplethin-film layers. In an example embodiment, the thickness of the ARcoating is chosen to be equal to or substantially equal to ¼ of thewavelength of emitted light as measured within the material constitutingthe AR coating. In an example embodiment, the wavelength of light is1100 nm and the AR coating includes SiN.

The structure resulting from the above-described method is an Si— orSi/Ge— based light-emitting device 120. In one example embodiment,reflective layer 50 and AR coating 100 have reflectivities designed tomake the light-emitting device operate as a laser diode (LD). In anotherexample embodiment, reflective layer 50 and AR coating 100 havereflectivities designed to make light-emitting device 120 operate as anon-coherent light-emitting diode (LED).

With continuing reference to FIG. 7, an example embodiment oflight-emitting device 120 with n+ and p+ doped regions operates asfollows. A voltage from a voltage source 124 is applied across metalcontacts 80 and 82. This causes electrons 130 to diffuse through thesubstrate away from (n+) doped region 60 and holes 132 to diffusethrough the substrate away from (p+) doped region 62. Within thesubstrate, recombination of electrons and holes occurs. For indirectbandgap materials such as Si and Si/Ge, the electron-hole pairs normallydiffuse a long time before radiative recombination occurs. In addition,bulk, surface, and contact non-radiative recombinations occur that canoverwhelm the radiative recombinations.

In light-emitting device 120, the sources of non-radiative recombinationare reduced so that light 94 is emitted via radiative recombinations. Inthis sense, the light-emitting device of the present invention hasproperties in common with a solar cell—namely, use of a float-zonesubstrate and the reduction of surface, contact and bulk-defectnon-radiative recombination effects. The main differences between thepresent invention and a solar cell (besides the emission vs. receptionof light) is that the present invention has the doped regions formed inthe upper surface as opposed to the upper and lower surfaces, usesminimal surface area for the contacts, and has an AR coating designedfor the wavelength of light emitted by the device based on the bandgapof Si or Si/Ge, rather than based on the reception of sunlightwavelengths.

The result is that light-emitting device 120 has an efficiency, definedas the percentage ratio of the “power in” to the “power out” (e.g., inWatts), of about 0.25% or greater. This level of efficiency makes theindirect bandgap light-emitting device of the present invention a viableintegrated light source for performing on-chip and chip-to-chipcommunication.

In example embodiment discussed in greater detail below in connectionwith FIG. 10, a modulator (406) can be placed downstream of thelight-emitting device to quickly switch the light beam. Reflection of alight beam or re-routing of a light beam can be achieved by applying avoltage to the modulator. Semiconductor modulators are typically capableof operating at high speeds and can be integrated with other electronicdevices, such as those discussed below.

On-Chip Communication System

FIG. 8A is a plan view of an example embodiment of an on-chip opticalcommunication system 200 that uses the light-emitting device of FIG. 7.System 200 is formed in a chip 204 with an upper surface 206. FIG. 8B iscross-sectional view of system 200.

System 200 includes the light-emitting device 120 formed integral withthe chip and operating in the present example embodiment as an LD(hereinafter, “LD 120”). Light-emitting device 150 can also be employedin system 200, and LD 120 is chosen for illustration purposes. LD 120 iselectrically connected via a wire 208 to a driver 210. An input voltageV_(IN) is provided to the driver.

System 200 includes an optical waveguide 220 formed on or in uppersurface 206. The optical waveguide includes an input end 222 and anoutput end 224. Optical waveguide 220 is optically coupled at the inputend to LD 120. In an example embodiment, the optical coupling isachieved using an optical coupler device 226, such as a prism, agrating, a lens, a mirror, or any combination thereof. LD device 120,driver 210 and optical coupler device 226 constitute alight-transmitting portion 228 of system 200.

In an example embodiment, the optical waveguide is part of a polymerwaveguide sheet laminated to upper surface 206. Polymer waveguides areparticularly well suited for transmitting light of infrared wavelength(e.g., 0.850 microns to about 1.55 microns), which are commonly usedwavelengths for chip-to-chip and other optical telecommunicationsapplications. Suitable polymer waveguide sheets are available fromOptical Crosslinks, Inc., Kennet Square, Pa.

In another example embodiment, optical waveguide 220 is formed in thesurface of the chip. FIG. 9A is an example embodiment of forming achannel optical waveguide for system 200 (FIG. 8A). With reference toFIG. 9A, one such technique includes forming a channel 230 in the uppersurface and lining the channel with a low-index material 232, such as alow-index polyimide. The lined channel is then filled with a high-indexcladding layer 234, such as a high-index polyimide. Another layer oflow-index material 232 is then deposited atop the high-index layer tocomplete the cladding.

FIG. 9B is another example embodiment of forming the optical waveguidefor system 200. With reference to FIG. 9B, the technique for formingoptical waveguide 220 involves depositing a first layer 250 ofhigh-index core material atop upper surface 206, patterning the firstlayer to form a high-index waveguide core 252, and then depositing alow-index cladding layer 254 atop the waveguide core.

FIG. 9C is an example embodiment of forming the optical waveguide forsystem 200 using a photosensitive polymer. With reference to FIG. 9C,the technique for forming optical waveguide 220 involves depositing alayer 280 of photosensitive polymer that undergoes a change inrefractive index when exposed to a select wavelength of radiation. Anexample polymer is acrylate, available from Dupont, Inc., Wilmington,Del. The waveguide array is then formed by selectively irradiating thephotosensitive polymer (e.g., by masking the layer 280) with radiation286 of the select wavelength to form a high-index region 290 withinlayer 280. Additional low-index material from layer 280 is then formedatop the structure to complete the cladding.

With reference again to FIGS. 8A and 8B, output end 224 of opticalwavguide 220 is optically coupled to a photodetector 310 formed integralwith chip 204. In an example embodiment, the optical coupling isachieved using an optical coupler device 320, such as a prism, agrating, a lens, a mirror, or any combination thereof. Photodetector 310is electrically connected via wire 322 to a transimpedance amplifier330, which in turn is connected to a post-amplifier 340 via wire 342.Optical coupler device 224, photodetector 310 and transimpedanceamplifier 330 constitute a light-receiving portion 346 of system 200.

In operation, driver 210 receives input voltage V_(IN) and in responsethereto, drives LD 120 to output a modulated optical signal 350. Opticalsignal 350 is coupled into optical waveguide 220 and travels down thewaveguide where it is received and detected by photodetector 310. Thephotodetector outputs a photodetector current signal 354 correspondingto optical signal 350. Current signal 354 travels to transimpedanceamplifier 330, which converts the current signal to a voltage signal356. This voltage signal is then amplified by post-amplifier 340 andoutputted therefrom as V_(OUT).

FIG. 10 is a close-up plan view of the light-emitting portion 228 ofanother example embodiment of an on-chip optical communication system400 as an alternate embodiment of system 200, where the light-emittingdevice is an LED and where the system includes an optical modulator tomodulate the light from the LED. In system 400, light-emitting device120 operates as an LED (hereinafter, LED 120). Further, an opticalmodulator 406 is arranged adjacent the LED output (e.g., in the opticalwaveguide). Also, LED 120 is electrically connected to a direct current(DC) voltage V_(DC) and produces a continuous DC output beam 420. System200 further includes a driver 430 electrically connected to opticalmodulator 406 and to V_(IN). In an example embodiment, input voltageV_(IN) is provided by an on-chip device 434, such as a CPU.

In operation, driver 430 drives the optical modulator in response toV_(IN), thereby creating a modulated output beam 450 from continuousoutput beam 420. The modulated output beam then travels down opticalwaveguide 220. The rest of the system and its operation is the same asthat of system 200, described above.

FIG. 11 is a plan view of multiple optical communication systems 200 or400 formed on an IC chip 200. The multiple systems provide for multiplecommunication paths on the chip.

Chip-to-Chip Communication System

FIG. 12A is a plan view of a chip-to-chip communication system 500 thatuses light-emitting device 120 (FIG. 7), while FIG. 12B is a side viewof system 500. System 500 is formed on a chip-bearing substrate 504having an upper surface 506. In one example embodiment of system 500,the chip-bearing substrate is a printed circuit board (PCB). In anotherexample embodiment, the chip-bearing substrate is an interposer, whichis a passive device containing wiring that provide a spatialtransformation between the closely spaced leads of an IC chip and themore widely spaced contacts of a PCB.

System 500 includes an IC chip 520 with a lower surface 522 and externalleads 524 connected to contacts 540 formed on the upper surface of thechip-bearing substrate. Contacts 540 are connected to wires 550 formedeither on the upper surface of the chip-bearing substrate (as with aPCB, as shown), or formed internal to the substrate (as with aninterposer). In an example embodiment, leads 524 are pins and contacts540 are holes, while in another example embodiment, the leads are solderballs and the contacts are pads to which the solder balls are flip-chipbonded. In an example embodiment, leads 524 are contacted to contacts540 such that IC chip lower surface 522 and upper surface 506 of thechip-bearing substrate are separated by a gap 560.

IC chip 520 includes, in an example embodiment, light-emitting device120 operating as a laser (i.e., LD 120), and driver 210 connectedthereto, as described above in connection with system 200. Power to thechip is provided by one of the wires 550 connected to a power supply(not shown). In an example embodiment, V_(IN) is provided from anotherdevice 434, such as a CPU, formed integral with the IC chip. In anexample embodiment, driver 210 includes a CPU.

System 500 includes an optical waveguide 580 with an input end 582 andan output end 584 formed on surface 506 of the chip-bearing substrate.Optical waveguide 580 is essentially the same as optical waveguide 220and can be formed on or in surface 506 using the same methods asdescribed above for forming waveguide 220 as discussed in connectionwith FIGS. 9A, 9B and 9C. Optical waveguide 580 is optically coupled atthe input end to LD 120. In an example embodiment, the optical couplingis achieved using an optical coupler device, such as a grating 590, alens 592, a bevel 594, or any combination thereof.

System 500 further includes an IC chip 620 with a lower surface 622 andexternal leads 624 connected to contacts 640 formed on the upper surfaceof the chip-bearing substrate. Contacts 640 are connected to wires 650formed either on the upper surface of the chip-bearing substrate (aswith a PCB, as shown), or formed internal to the substrate (as with aninterposer). In an example embodiment, leads 624 are pins and contacts640 are holes, while in another example embodiment, the leads are solderballs and the contacts are pads to which the solder balls are flip-chipbonded. In an example embodiment, leads 624 are contacted to contacts640 such that IC chip lower surface 622 and upper surface 506 of thechip-bearing substrate are separated by a gap 660.

IC chip 620 includes, in an example embodiment, photodetector 310connected to transimpedance amplifier 330, which in turn is connected topost-amplifier 340, as described above in connection with system 200.Photodetector 310 of IC chip 620 is optically coupled to output end 584of optical waveguide 580. In an example embodiment, the optical couplingis achieved using an optical coupler device, such as a grating 690, alens 692, a bevel 694, or any combination thereof.

In operation, driver 210 receives input voltage V_(IN) and in responsethereto, drives LD 120 to output a modulated optical signal 750.Modulation can also be achieved by using a separate optical modulatorsuch as modulator 406 (FIG. 10). Optical signal 750 is coupled intooptical waveguide 580 and travels down the waveguide where it isreceived and detected by photodetector 310. The photodetector outputs aphotodetector current signal 770 that travels to transimpedanceamplifier 330, which converts the output current signal to a voltagesignal 776. The voltage signal is then amplified by post-amplifier 340and outputted therefrom as V_(OUT). The voltage signal V_(OUT) is thenavailable for processing by another device in the chip, such as CPU 790.

The various elements depicted in the drawings are merelyrepresentational and are not drawn to scale. Certain proportions thereofmay be exaggerated, while others may be minimized. The drawings areintended to illustrate various implementations of the invention, whichcan be understood and appropriately carried out by those of ordinaryskill in the art.

While certain elements have been described herein relative to “upper”and “lower”, and “horizontal” and “vertical”, it will be understood thatthese descriptors are relative, and that they could be reversed if theelements were inverted, rotated, or mirrored. Therefore, these terms arenot intended to be limiting.

It is emphasized that the Abstract is provided to comply with 37 C.F.R.§1.72(b) requiring an Abstract that will allow the reader to quicklyascertain the nature and gist of the technical disclosure. It issubmitted with the understanding that it will not be used to interpretor limit the scope or meaning of the claims.

In the foregoing Detailed Description, various features are groupedtogether in various example embodiment for the purpose of streamliningthe disclosure. This method of disclosure is not to be interpreted asreflecting an intention that the claimed embodiments of the inventionrequire more features than are expressly recited in each claim. Rather,as the following claims reflect, inventive subject matter lies in lessthan all features of a single disclosed embodiment. Thus the followingclaims are hereby incorporated into the Detailed Description, with eachclaim standing on its own as a separate preferred embodiment.

While the present invention has been described in connection withpreferred embodiments, it will be understood that it is not so limited.On the contrary, it is intended to cover all alternatives, modificationsand equivalents as may be included within the spirit and scope of theinvention as defined in the appended claims.

1. A method of forming a light-emitting device comprising: providing asubstrate made of float-zone Si or float-zone Si/Ge; forming andielectric layer on a lower substrate surface and a reflective layeratop the dielectric layer; forming spaced apart doped regions in anupper substrate surface; texturing a portion of the substrate surfacebetween the doped regions; forming first and second metal contactingrespective portions of the doped regions.
 2. The method of claim 1,further including forming an antireflection coating over the texturedportion.
 3. The method of claim 2, including forming the antireflectioncoating and the reflective layer to have reflectivities such that thelight-emitting device operates as a laser diode.
 4. The method of claim2, including forming the antireflection coating and the reflective layerto have reflectivities such that the light-emitting device operates as anon-coherent light-emitting diode.
 5. The method of claim 1, includingforming an optical waveguide optically coupled to the textured portion.6. The method of claim 5 including forming an optical coupler devicebetween the textured portion and the optical waveguide.
 7. The method ofclaim 5 including forming an optical coupler device between theantireflection coating and one end of the optical waveguide.
 8. Themethod of claim 7 including forming a further optical coupler devicebetween another end of the optical waveguide and a photodiode tooptically couple the laser diode to the photodiode.
 9. A light-emittingdevice comprising: a substrate formed from a float-zone semiconductormaterial; a dielectric layer formed on a lower substrate surface and areflective layer formed atop the dielectric layer; spaced apart dopedregions formed in an upper substrate surface, with a textured surfaceportion formed between the doped regions; first and second metalcontacts that contact respective portions of the doped regions; anantireflection coating formed over the textured surface portion; and anoptical waveguide optically coupled to the textured surface portion. 10.The light-emitting device of claim 9, wherein the antireflection coatingand the reflective layer have reflectivities such that thelight-emitting device is operable as a non-coherent light-emittingdiode.
 11. The light-emitting device of claim 9, wherein theantireflection coating and the reflective layer have reflectivities suchthat the light-emitting device is operable as a laser diode.
 12. Thelight-emitting device of claim 9, wherein the light-emitting device iscapable of emitting light having a wavelength of about 1100 nm.
 13. Thelight-emitting device of claim 9, further including an antireflectivecoating formed over the roughened surface portion, the antireflectioncoating having a thickness equal to or substantially equal to ¼ of awavelength of light emitted by the light-emitting device.
 14. Thelight-emitting device of claim 9, wherein the first and second metalcontacts have a contact surface area that is 1% or less of a total uppersurface area of the light-emitting device.
 15. A system comprising: asubstrate formed from float-zone Si or float-zone Si/Ge; an indirectbandgap light-emitting device formed integral with the substrate, thelight emitting device including an antireflective coating formed atop orwithin an upper surface of the substrate; an optical waveguide formedabove the antireflective coating and optically coupled at a firstwaveguide end to the light-emitting device; and a photodiode formedintegral with the substrate and optically coupled to a second waveguideend of the optical waveguide.
 16. The system of claim 15, wherein thelight-emitting device includes: a reflective layer formed adjacent aportion of a substrate lower surface and insulated from the lowersurface by an dielectric layer; spaced apart doped regions formed in anupper substrate surface with an antireflection-coated textured surfaceportion formed therebetween; and first and second metal contactsrespectively contacting a portion of the doped regions.
 17. The systemof claim 16, further including a driver electrically connected to thelight-emitting device.
 18. The system of claim 17, further including atransimpedance amplifier formed integral with the substrate andelectrically connected to the photodiode.
 19. The system of claim 18,further including a post-amplifier formed integral with the substrateand electrically connected to the transimpedance amplifier.
 20. Thesystem of claim 15, including first and second optical coupler devicesat or near the respective first and second waveguide ends, the firstoptical coupler adapted to couple light from the light-emitting deviceinto the optical waveguide, and the second optical coupler deviceadapted to couple light from the optical waveguide to the photodiode.21. The system of claim 15, further including: an optical modulatorarranged downstream of the light-emitting device; and a driverelectrically connected to the optical modulator.
 22. The system of claim15, wherein the light-emitting device is adapted to operate as alight-emitting diode and provide a continuous output beam.
 23. A system,comprising: a chip-bearing substrate with an upper surface; a first ICchip formed from a float-zone Si or float-zone Si/Ge substrate andelectrically connected to the chip-bearing substrate, the first IC chipincluding an indirect-bandgap light-emitting device formed integral withthe substrate; an antireflection coating formed above the substrate andoptically coupled to the light-emitting device; an optical waveguideformed above the antireflection coating optically coupled at a firstwaveguide end to the light-emitting device; and a second IC chipelectrically connected to the substrate and having a photodiodeoptically coupled to a second waveguide end.
 24. The system of claim 23,wherein the light-emitting device includes: a reflective layer formedadjacent a portion of a substrate lower surface and insulated from thelower surface by an dielectric layer; spaced apart doped regions formedin an upper substrate surface with an antireflection-coated texturedsurface portion formed therebetween; and first and second metal contactsrespectively contacting a portion of the doped regions.
 25. The systemof claim 23, wherein the first IC chip includes a driver electricallyconnected to the light-emitting device.
 26. The system of claim 25,wherein the first IC chip includes a CPU electrically connected to thedriver.
 27. The system of claim 23, further including: an opticalmodulator arranged downstream of the light-emitting device; and a driverelectrically connected to the optical modulator.
 28. The system of claim27, wherein the light-emitting device is adapted to operate as alight-emitting diode and provide a continuous output beam.